Title page for ETD etd-10142005-103113

The development of poly(vinylidene fluoride) piezoelectric sensors for measuring peel stresses in adhesive joints

Degree

PhD

Department

Engineering Science and Mechanics

Advisory Committee

Advisor Name

Title

Dillard, David A.

Committee Chair

Hendricks, Scott L.

Committee Member

Henneke, Edmund G. II

Committee Member

Mook, Dean T.

Committee Member

Wightman, James P.

Committee Member

Keywords

Strain gages

Piezoelectric materials

Detectors

Adhesive joints testing

Date of Defense

1992-02-04

Availability

restricted

Abstract

Although bond-normal stresses have been shown to be responsible for the
failure of most laboratory adhesive joint geometries, the measurement of these stresses
has been accomplished only through the use of very sophisticated optical techniques.
In order to develop a more versatile measurement technique, poly(vinylidene fluoride)
film was used to develop piezoelectric stress sensors. The sensitivities of the film to
normal stresses in the three principal material directions of the orthotropic film were
accurately measured using a charge amplifier and a storage oscilloscope. These
measured sensitivities comprised the calibration constants of the film.

In order to reduce the detrimental effect on bond strength caused by embedding
the low surface energy film into adhesive bondlines, surface treatment methods were
investigated using contact angle studies, XPS analysis and 1800 peel and tapered
double cantilever beam adhesion specimens. An acid etch using a mixture of acetic,
phosphoric and nitric acids was found to greatly improve the bond strengths to an
epoxy adhesive without reducing the piezoelectric activity of the film.

The bond-normal stresses in both the elastomeric butt joint and the single lap
shear joint were measured using the developed stress sensors. Comparison of the
measured stresses with calculated values obtained from closed-form analytical
solutions and finite element analysis for the stresses was excellent.

The piezoelectric sensors do have several important limitations. The
piezoelectric activity of the film is lost at temperatures above 100°C (210°F). Also,
the sensors are only sensitive to dynamic loads. Nonetheless, the sensors provide an
accurate means of measuring peel stresses in many adhesive joints of practical interest.